Separately supported polymetallic reforming catalyst

ABSTRACT

There is provided, in accordance with the present invention, a catalyst composition made up of a mixture of two components, one component comprising a minor proportion of platinum and rhenium on a support and the second component comprising a minor proportion of iridium and rhenium on a separate support. A process for reforming a charge stock, such as naphtha, utilizing such catalyst is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 525,778, filedAug. 24, 1983.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a catalyst composition containing platinum,rhenium and iridium where (1) platinum and rhenium and (2) iridium andrhenium are contained on separate particles of a refractory support andto the reforming of selected petroleum fractions in the presence of thiscatalyst to obtain gasoline of high octane number.

2. Description of the Prior Art

Catalysts intended for use in reforming operations wherein hydrocarbonfractions such as naphthas or gasolines or mixtures thereof are treatedto improve the anti-knock characteristics thereof are well known in thepetroleum industry and have been the subject of intensive investigationin both the patent and technical literature.

It has heretofore been proposed to employ platinum metal-containingcatalysts for promoting reforming. Such catalysts are necessarilycharacterized by a certain amount of acidity. One type of reformingcatalyst which has been used commercially consists of alumina basematerial having platinum metal impregnated thereon, with the aciditycharacteristics being contributed by a small amount of halogenincorporated in the catalyst.

In more recent years, multi-metallic reforming catalysts have been thesubject of patent and technical literature. These catalysts containplatinum together with one or more additional metals, such as ruthenium,germanium, iridium, palladium, rhenium, osmium, rhodium, copper, silver,tin or gold deposited on a refractory support which also contains aspecified amount of halogen. Representative of these multi-metallicreforming catalysts are those containing platinum and rhenium onplatinum and iridium such as described in U.S. Pat. Nos. 2,848,377;3,415,737 and 3,953,368. The latter patent reports certain advantageswhen platinum and iridium are present on a refractory support as highlydispersed polymetallic clusters in which the metallic atoms areseparated by a distance of about 2.5-4.0 Angstroms.

It has also heretofore been known to conduct catalytic reformingutilizing a catalyst consisting essentially of a particularly definedmixture of particles of a porous carrier impregnated with a small amountof platinum and particles of an acidic cracking component.Representative disclosures of such prior art are found in U.S. Pat. Nos.2,854,400; 2,854,403; 2,854,404. Also, it has been suggested, forexample, in German OS No. 26 27 822 to conduct reforming in the presenceof a catalyst constituting a mixture of platinum on one solid catalystand rhenium on a second solid carrier.

The use of trimetallic catalysts is also known in the reforming art and,in fact, single particle platinum, rhenium, and iridium catalysts on analumina support are specifically taught in U.S. Pat. Nos. 3,578,583;3,617,520; 3,487,009; as well as an article in International ChemicalEngineering, 1978.

Recently, there have been advances made in the art on using separateparticles containing platinum and rhenium on one support and iridium onanother support. Patents of this general type are U.S. Pat. No.4,288,348; as well as U.S. Pat. No. 4,264,475. All of the abovecatalysts, while possessing certain advantages, are nevertheless subjectto improvement with regard to the provision of a reforming catalystwhich provides a high yield of gasoline of high octane number over anextended period of time.

SUMMARY OF THE INVENTION

In accordance with the invention described herein, reforming of ahydrocarbon charge such as naphtha can be effectively carried out overan extended period of time under conditions of high severity to producea high yield of gasoline of high octane number when the reforming isconducted in the presence of a catalyst which is a modification of theseparately supported polymetallic catalysts described and claimed inU.S. Pat. Nos. 4,288,348 and 4,264,475--the disclosure of both saidpatents being incorporated by reference.

U.S. Pat. No. 4,288,348 discloses catalyst compositions and the use ofthe same in reforming which contain platinum, rhenium and iridium where(1) platinum and rhenium and (2) iridium are contained on separateparticles of a refractory support.

It has now been found that improved results with respect to hydrogenpurity and C₅ + yields together with decreased methane and ethaneproduction can be achieved with significant yield stability improvementsif the iridium containing component also contains rhenium. In additionto the above-listed benefits, the use of a rhenium promoter with iridiumenables the catalyst composition to perform under conditions which aremore severe than are possible with a catalyst containing an unpromotedcatalyst particle.

It is specifically noted that at column 5, lines 5-23 of said U.S. Pat.No. 4,288,348 the following appears:

While, as above described, it is a preferred embodiment of the inventiondescribed herein that the present reforming catalyst consist essentiallyof a mixture of a minor proportion of platinum-rhenium on a support anda minor proportion of iridium on a separate support, the catalyst mayoptionally contain in addition to platinum-rhenium and iridium, one orseveral additional catalytic components such as silver osmium, copper,gold, palladium, rhodium, gallium, germanium, tin or compounds thereofon one support containing platinum-rhenium and one or more suchadditional catalytic components on a second support, which also containsthe iridium. The amounts of the added catalytic components may be in theapproximate range of 0.01 to 1 weight percent, preferably between about0.1 and about 1.0 weight percent. The platinum content, rhenium content,iridium content and halogen content of the catalysts is in the samerange as set forth hereinabove, with the preferred support beingalumina.

As can be seen, although said patent envisions modification of theiridium-containing support with various catalytically active metals,rhenium is not specifically mentioned.

U.S. Pat. No. 4,264,475 discloses the following at column 4, lines45-62:

While, as above described, it is a preferred embodiment of the inventiondescribed herein that the present reforming catalyst consist essentiallyof a mixture of a minor proportion of platinum on a support and a minorproportion of iridium on a separate support, the catalyst may optionallycontain in addition to platinum and iridium, one or several additionalcatalytic components such as silver osmium, copper, gold, palladium,rhodium, gallium, rhenium, germanium or tin or compounds thereof on onesupport and one or more such additional catalytic components on a secondsupport which also contains the iridium. The amounts of the addedcatalytic components may be in the approximate range of 0.01 to 2 weightpercent, preferably between about 0.1 and about 1.0 weight percent. Theplatinum content, iridium content and halogen content of catalysts is inthe same range as set forth hereinabove, with the preferred supportbeing alumina.

As can be seen, although there is a broad teaching of promoting both theplatinum-containing component and the iridium-containing component withvarious metals including rhenium, there is no specific teaching ofpromoting both components with rhenium, particularly at the levels whichwill be later described.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The separately supported polymetallic reforming catalysts of thisinvention comprise a mixture of (1) platinum and rhenium on anappropriate support and (2) iridium and rhenium on an appropriatesupport. The platinum and iridium individually can range from 0.05 to 5%by weight based on the total composition whereas the rhenium can rangefrom 0.2 to 0.6 based on the total composition. The particularlypreferred catalyst contains 0.3% by weight of each of platinum, rheniumand iridium.

The refractory support for utilization in the instant invention is aporous adsorptive material having a surface area exceeding 20 squaremeters per gram and preferably greater than about 100 square meters pergram. Refractory inorganic oxides are preferred supports, particularlyalumina or mixtures thereof with silica. Alumina is particularlypreferred and may be used in a large variety of forms including aluminaprecipitate or gel, alumina monohydrate, sintered alumina and the like.Various forms of alumina either singly or in combination, such as eta,chi, gamma, theta, delta or alpha alumina may be suitably employed asthe alumina support. Preferably, the alumina is gamma alumina and/or etaalumina. The above nomenclature used in the present specification andclaims with reference to alumina phase designation is that generallyemployed in the United States and described in The Aluminum Industry:Aluminum and Its Production by Edwards, Frary and Jeffries, published byMcGraw-Hill (1930). The refractory support, desirably alumina has apreferred particle size of at least 0.01 microns and generally notexceeding about 3000 microns. The alumina may be employed in massiveform but generally will be in the form of a powder or in particle form,either irregularly shaped or uniformly shaped as beads, cubes, tablets,extruded pellets, and the like. In the preparation of spheroidal aluminagel particles, an alumina hydrosol is prepared by intimate admixture ofsuitable reactants and the hydrosol is introduced in the form ofglobules to a water-immiscible medium, the depth and temperature ofwhich is controlled so that the hydrosol globules set for spheroidalparticles of hydrogel during passage through said medium. The resultinghydrogel particles are thereafter withdrawn from the forming zone andconducted to suitable washing, drying and/or calcining equipment asdescribed. Alumina, in the form of a precipitate, may be prepared byadding a suitable reagent such as ammonium hydroxide or ammoniumcarbonate to an aluminum salt such as aluminum chloride, aluminumnitrate, aluminum acetate, etc. in an amount to form aluminum hydroxidewhich, upon drying, is converted to alumina. After the alumina has beenformed, it is generally washed to remove soluble impurities. Washingprocedures ordinarily involve washing with water, either in combinationwith filtration or as separate operations. It has been found thatfiltration of the alumina is improved when the wash water contains asmall amount of ammonium hydroxide. The extent of washing will depend tosome extent on the nature of the reactants initially employed inpreparation of the alumina precipitate.

Halogen may be added to the support, preferably alumina, in a form whichwill readily react therewith in order to obtain the desired results. Onefeasible method of adding the halogen is in the form of an acid, such ashydrogen fluoride, hydrogen bromide, hydrogen chloride and/or hydrogeniodide. Other suitable sources of halogen include volatile salts, suchas ammonium fluoride, ammonium chloride and the like. When such saltsare used, the ammonium ions will be removed during subsequent heating ofthe catalyst. Halogen may also be added as fluorine, chlorine, bromineor iodine or by treatment in gaseous hydrogen halide. The halogen,preferably a chlorine or fluorine moiety, may be incorporated into thecatalyst at any suitable stage in the catalyst manufacture. Thus,halogen may be added before, after or during incorporation of the metalor metals. It is preferred to introduce halogen during impregnation withthe metal or metals after the alumina has undergone carbon dioxidetreatment. One method to accomplish this is to use halogen-containingmetal compounds, such as chloroplatinic acid or chloroiridic acid.Additional amounts of halogen may be incorporated in the catalyst bycontacting it with materials, such as hydrogen fluoride and hydrogenchloride, either prior to or subsequent to the metal impregnation step.Halogen may also be incorporated by contacting the catalyst with agaseous stream containing the halogen, such as chlorine or hydrogenchloride. One feasible way to halogenate the alumina is by the additionof an alkyl halide, such as tertiary butyl chloride during the reformingoperation. The amount of halogen introduced into the support is suchthat the halogen content of the overall catalyst is between about 0.1and about 5 weight percent.

It is an essential feature of the present invention that the aluminabase be pretreated with gaseous carbon dioxide prior to impregnationwith a solution containing the desired metal or metals. The alumina baseeither with or without halogen is dried to a water content preferably ofless than 30 percent by weight. It is particularly preferred that thealumina base, after drying, be calcined before contact thereof withgaseous carbon dioxide. The dried and/or calcined alumina is thereafter,in accordance with the process of this invention, treated with gaseouscarbon dioxide. Such treatment is generally effected under roomtemperature conditions utilizing a carbon dioxide pressure in the rangeof between about 100 kPa (0 psig) and 450 kPa (50 psig). The alumina isgenerally treated with carbon dioxide for a period between about oneminute and about 48 hours and more usually between about one minute andabout 3 hours. It is to be noted that the time of gas treatment and thegauge pressures set forth above are not considered critical, it beingonly necessary that the alumina base be exposed to a gaseous carbondioxide atmosphere for a sufficient period of time and under sufficientpressure to become substantially saturated. The gas initially containedin the pores of the alumina base, which will ordinarily be air, may bereplaced by sweeping the alumina particles with gaseous carbon dioxidefor a sufficient period of time to replace substantially all of the airin the pores of the alumina with carbon dioxide. It is generallypreferred, however, to subject the porous alumina base to a vacuum,thereby removing the air or other gas contained therein and subsequentlyto contact the evacuated particles with gaseous carbon dioxide. Thealumina, after treatment with carbon dioxide, is thereafter impregnatedwith a solution of a suitable compound(s) of the desired metal ormetals. In one preferred embodiment of the invention, the alumina, afterpretreatment, is maintained in an atmosphere of gaseous carbon dioxideduring the subsequent impregnation. Desirably, the alumina which hasundergone pretreatment with gaseous carbon dioxide should be broughtinto contact with the impregnating solution containing compound(s) ofthe desired metal or metals immediately after such pretreatment toinsure the optimum results of this invention.

A particularly effective method of impregnating the carbon dioxidetreated alumina support comprises the use of an aqueous solution ofmetal containing acids such as chloroplatinic acid, bromoplatinic acid,chloroiridic acid, perrhenic acid (HReO₄), etc. A particularly preferredembodiment of this invention involves the preparation of a catalystcomprising Pt-Re on alumina and iridium-rhenium on alumina. In thepreparation of such a catalyst two general procedures can be followed.One procedure involves separately treating one alumina support with anaqueous solution of chloroplatinic acid and perrhenic acid and anotheralumina support with an aqueous solution of chloroiridic acid andperrhenic acid, and then blending the aluminas.

Another procedure involves separately treating one alumina support withan aqueous solution of chloroplatinic acid and another alumina supportwith an aqueous solution of chloriridic acid, blending the two aluminastogether and treating the blended mixture with an aqueous solution ofperrhenic acid.

Irrespective of the method employed the appropriate aqueous acidsolution is commingled with the carbon dioxide treated alumina particlesand the resulting mixture is permitted to stand, preferably with orafter suitable agitation, so that thorough mixing is obtained and evendistribution of the platinum, iridium, and rhenium solutions throughoutthe alumina supports is attained. This period of contact will generallybe in the approximate range of between about 10 minutes and 48 hours,and more generally between about 10 minutes and 2 hours. Solutions ofother compound which may also be suitably employed for impregnationinclude platinum tetrachloride, ammonium platinum chloride, trimethylbenzyl ammonium platinum chloride, tetraamineplatinum (II) chloride,ammonium platinum nitrate, dinitrodiamineplatinum (II), ammoniumperrhenate, perrhenic acid (HReO₄), ammonium perrhenate (NH₄ ReO₄),iridium compounds such as the ammonium chloride double salt, tribromide,trichloride, tetrachloride or chloroiridic acid. Iridium amine complexesmay also be suitably employed.

The resulting composites of aluminas and the metals with the combinedhalogen is dried at a temperature of between about 93° C. (200° F.) and260° C. (500° F.) for a period of time between about 0.5 hours and 24hours or longer and thereafter the composite is calcined in the presenceof an oxygen containing gas, e.g. air, at a temperature of between about430° C. (800° F.) and 540° C. (1000° F.) for a period of time of betweenabout 0.5 hour and 12 hours or more. In some instances, said calcinationmay occur in nitrogen in lieu of air. In addition to calcination, thecomposite may be exposed in a hydrogen atmosphere to reduce asubstantial portion of the metal components to the elemental state. Suchreduction is generally conducted at temperatures not in excess of 540°C. (1000° F.).

The relative weight ratio of the separate particles containingplatinum-rhenium and those containing iridium-rhenium is generallybetween about 10:1 and about 1:10. The dimensions of the separateparticles may range from powder size, e.g. 0.01 micron up to particlesof substantial size, e.g. 10,000 microns. Preferably, the particle sizeis between about 1 and about 3000 microns.

In a particular embodiment of the method of this invention, aluminabeads are pretreated with gaseous carbon dioxide, then, while said beadsare mixed by continuous rotation, the beads are impregnated with theappropriate aqueous solutions containing a compound (or complex orcomplexes) of the desired metals followed by drying and calcination.Post impregnation carbon dioxide treatment may be utilized as aprecaution.

The catalyst prepared according to the novel method of the instantinvention is particularly useful in the reforming of hydrocarbons.Charge stocks undergoing reforming, using the catalysts describedherein, are contemplated as those conventionally employed. These includevirgin naphtha, cracked naphtha, gasoline, including FCC gasoline, ormixtures thereof boiling within the approximate range of 20° C. (70° F.)to 260° C. (500° F.) and, preferably within the range of about 50° C.(120° F.) to about 235° C. (450° F.). The charge stock is contacted inthe vapor phase with the catalyst at a liquid hourly space velocitybetween about 0.1 and about 10 and preferably between 0.5 and about 4.Reaction temperature is within the approximate range of 370° C. (700°F.) to 590° C. (1100° F.) and preferably between about 430° C. (800° F.)and about 565° C. (1050° F.). Hydrogen may be added to the reaction zoneat a rate corresponding to a mole ratio of hydrogen to hydrocarboncharge of between about 0.5 and about 20 and preferably between about 2and 12. Reaction pressure is maintained between about 450 kPa (50 psig)and 7000 kPa (1000 psig), preferably between about 795 kPa (100 psig)and 4935 kPa (700 psig). Since the reforming process produces largequantities of hydrogen, at least a portion thereof may be convenientlyemployed for the introduction of hydrogen with the feed.

It is contemplated that the resultant catalyst of the method of thisinstant invention may be employed in any of the conventional types ofprocessing equipment. Thus, the catalyst may be used in the form ofpills, pellets, extrudates, spheres, granules, broken fragments orvarious other shapes dispersed as a fixed bed within a reaction zone.The charge stock may be passed through the catalyst bed as a liquid,vapor or mixed phase in either upward or downward flow. The catalyst mayalso be used in a form suitable for moving beds. In such instance, thecharge stock and catalyst are contacted in a reforming zone wherein thecharge stock may be passed in concurrent or countercurrent flow to thecatalyst. Alternatively, a suspensoid-type process may be employed inwhich the catalyst is slurried in the charge stock and the resultingmixture conveyed to the reaction zone. The reforming process isgenerally carried out in a series of several reactors. Usually, three tofive reactors are used. The catalyst prepared according to the method ofthe invention may be employed in just one of the reactors, e.g. thefirst reactor or in several reactors or in all reactors. After reaction,the product from any of the above processes is separated from thecatalyst by known techniques and conducted to distillation columns wherethe various desired components are obtained by fractionation.

The following examples will now illustrate the best mode contemplatedfor carrying out the invention.

The supports used in the following examples were commercially obtainedspheroidal 1/16 inch gamma alumina beads. Typical analytical propertiesof these beads is given hereinbelow in Table 1. In general, the supportswere humidified before each preparation by storing over water in aclosed vessel for at least four hours. This humidification step can becombined with the carbon dioxide pretreatment step if so desired. Thehumidification step is not essential to achieve the beneficial resultsafforded by the instant invention. The use of humidification, however,depends on the state of hydration of the support.

                  TABLE 1                                                         ______________________________________                                        Typical Analytical Properties of γ-Al.sub.2 O.sub.3                     ______________________________________                                        Beads                                                                         Density, Real, g/cc  2.94                                                     Particle, g/cc       0.76                                                     Pore Volume, cc/g    0.97                                                     Surface Area m.sup.2 /g                                                                            195                                                      % SiO.sub.2          0.35                                                     % Na                 0.02                                                     % Cl                 0.04                                                     Crystallinity        intermediate                                             (order-disorder)                                                              ______________________________________                                    

EXAMPLE 1

This example will illustrate the preparation of the separately supportedpolymetallic catalysts of this invention.

The catalyst composite contains 0.3 weight percent platinum, 0.2 weightpercent rhenium, and 0.3 weight percent iridium on alumina with carbondioxide presaturation of both alumina supports.

A double cone blender was filled with humidified γ-Al₂ O₃ beads. Theblender was attached to a rotary evaporator and was evacuated andbackfilled with CO₂. The blender was then rotated and, under a partialvacuum, the beads were impregnated with an aqueous solution of H₂ PtCl₆so as to provide 0.6 weight percent platinum. The impregnated beads wereheld under a CO₂ atmosphere for one hour and then dried.

A second sample of said alumina beads was similarly treated except thatH₂ IrCl₆ was used in an amount sufficient to provide a compositioncontaining 0.6 weight percent iridium. The two batches of impregnatedalumina particles were then mixed in a blender to yield a catalysthaving an overall composition of 0.3 weight percent platinum, 0.3 weightpercent iridium. The mixture of alumina particles was then treated withcarbon dioxide in the manner above set forth and contacted with anaqueous solution of HReO₄ so as to provide 0.2 weight percent Re.

The catalyst was pretreated at 850° F. using an O₂ /HCl mixture in N₂for two hours (5% O₂ /1% HCl) followed by reduction with H₂ for onehour. This catalyst containing 0.3 weight percent each of platinum andiridium and 0.2 weight percent of rhenium is identified as Catalyst A.

EXAMPLE 2

The process of Example 1 was repeated with the exception that enoughHReO₄ was used to obtain a catalyst containing 0.3 weight percent eachof Pt, Ir and Re.

This is identified as Catalyst B and is the most preferred.

EXAMPLE 3

The process of Example 1 was repeated with the exception that enoughHReO₄ was used to obtain a catalyst containing 0.3 weight percent eachof Pt and Ir and 0.6 weight percent Re.

This is identified as Catalyst C.

EXAMPLE 4

This is a comparison example outside the scope of this invention.

In this example, the procedure of Example 1 was repeated except that norhenium was introduced.

Thus, the catalyst consisted of a mixture of separate particles ofiridium-impregnated alumina and platinum impregnated alumina. Thecatalyst contained 0.3 weight percent each of platinum and iridium andis identified as Catalyst D.

EXAMPLE 5

This is a comparison example outside the scope of this invention.

This example is the catalyst of Example 1 of U.S. Pat. No. 4,288,348containing platinum-rhenium on a separate alumina support compositedwith iridium on a separate alumina support so as to obtain a catalysthaving 0.3 weight percent each of platinum, iridium and rhenium. Thecatalyst was pretreated in the same manner as Example 1.

This catalyst is identified as Catalyst E.

EXAMPLE 6

A commercially prepared platinum/rhenium reforming catalyst containing0.3 weight percent platinum and 0.3 weight percent rhenium on extrudedgamma alumina was identified as Catalyst F.

EXAMPLES 7-11

The catalysts prepared according to the general procedures of Examples1-5 each underwent a catalyst screening test using n-hexane and thecharge stock. The conditions for such screening tests were as follows:

    ______________________________________                                        Test conditions:  0.5 g catalyst                                                                H.sub.2 Reduction at 454° C.                         Dehydrocyclization:                                                                             Charge Stock n-hexane                                                         WHSV = 3 Hr.sup.-1                                                            H.sub.2 /HC = 7                                                               Temp. = 470° C.                                                        Time = 60 minutes                                           ______________________________________                                    

The screening test was conducted by first reducing the catalyst samplewith hydrogen at 454° C. and the temperature was raised to 470° C. andthen n-hexane was passed over the catalyst sample at the above-statedconditions for 60 minutes.

During the period at which the catalyst was contacted with normal hexanethe methane make and the benzene make were determined. The benzene makeis a direct measure of the dehydrocyclization activity of the catalystand, of course, the methane make determines the practical significanceof a catalyst in a reforming process since too high a methane makesignificantly reduces reformate yield and hydrogen production and canaccelerate catalyst aging.

The results obtained are shown in the following table.

                  TABLE 2                                                         ______________________________________                                        Catalyst Screening Test Results                                               Example      7       8      9      10   11                                    Catalyst     A       B      C      D    E                                     ______________________________________                                        Wt. % Pt     0.3     0.3    0.3    0.3  0.3                                   Wt. % Re     0.2     0.3    0.6    0.0  0.3                                   Wt. % Ir     0.3     0.3    0.3    0.3  0.3                                   nC.sub.6 % Conv.                                                                           53.0    64.2   47.2   62.7 57.8                                  Benzene Yield, %                                                                           9.7     9.7    8.8    11.7 10.5                                  Methane Yield, %                                                                           3.6     5.8    2.9    19.6 18.0                                  Benzene      18.3    15.1   18.6   18.7 18.2                                  Selectivity.sup.1                                                             Methane      6.8     9.0    6.1    31.3 31.1                                  Selectivity.sup.2                                                             ______________________________________                                         ##STR1##                                                                      ##STR2##                                                                                                                                               

The relative aromatization characteristics of catalysts are given by thebenzene yield and selectivity values, while the degree of hydrocrackingpromoted by them is manifested in the methane yield and selectivitydata.

The test results indicate that catalysts A, B and C improves theactivity of the catalyst and moderates the severe hydrocracking usuallyassociated with separate particle catalysts having an unpromoted iridiumcomponent such as Catalysts D and E.

EXAMPLES 12-15

The catalysts B, D, E and F above were further tested for reformingusing a full range naphtha with the following properties:

    ______________________________________                                        Properties                                                                    Gravity, API     61.8                                                         Specific Gravity 0.7365                                                       Sulfur, ppm      <0.2                                                         Nitrogen, ppm    <0.2                                                         Chloride, ppm    <1                                                           Distillation, °F.                                                      IBP              169                                                          10% vol.         201                                                          30%              223                                                          50%              253                                                          70%              286                                                          90%              320                                                          EP               354                                                          Composition, wt. %                                                            Paraffins        70.9                                                         Naphthenes       17.8                                                         Aromatics        11.2                                                         ______________________________________                                    

Reforming of the above charge was carried out in adiabatic three reactorsystem with recycle. Alcohol, organochloride, and sulfur was added tothe naphtha as indicated below to simulate exact commercial conditions.The other operating parameters are listed below with the comparisons.

                  TABLE 3                                                         ______________________________________                                        Yield Comparison of Various Iridium                                           Containing Catalysts                                                          Example      12       13       14     15                                      ______________________________________                                        Pressure, psig                                                                             200      → →                                                                             →                                TRR          6        → →                                                                             →                                WHSV         2        → →                                                                             →                                LHSV         1.4      → →                                                                             1.84                                    Sulfur, ppm  2        → →                                                                             →                                R + O        98       → →                                                                             →                                Catalyst     B        D        E      F                                       Days on Stream                                                                             21       21       21     21                                      RIT, °F.                                                                            977      1008     953    961                                     C.sub.5 + Yield, vol %                                                                     73.4     68       71.8   72                                      H.sub.2 Purity, mol %                                                                      71.9     51.7     67.2   68.7                                    H.sub.2 Prod., SCF/BBL                                                                     771      463      773    729                                     C.sub.1, wt. %                                                                             1.9      3.8      2.7    2.3                                     C.sub.2, wt. %                                                                             4.4      7.3      6.2    5.0                                     C.sub.3, wt. %                                                                             5.7      5.6      6.0    6.1                                     C.sub.4, wt. %                                                                             8.2      9.6      7.5    8.0                                     ______________________________________                                    

Catalyst B has a lower activity than Catalyst E. Despite its loweractivity Catalyst B has superior C₅ + yields and hydrogen purity overthat of the above mentioned catalysts. The hydrogen production ofCatalyst B is comparable to that of the trimetallic Catalyst E and muchhigher than Catalyst D. The higher C₅ + yields and yield stability ofCatalyst B over that of the unpromoted iridium catalysts is apparentfrom its lower methane and ethane yields. Such a low yield of C₁ -C₂gases is characteristic of Pt+Ir catalysts. The propane yields from allcatalysts are very similar.

The coke levels on the individual components of the spent Catalyst B arecompared with those of Catalyst D and Catalyst E. These results indicatethat the coke levels on Catalyst D are the highest despite its cyclelength being the shortest. Catalyst B results in a higher coke level onthe iridium component than Catalyst E despite its stable yields. Thiscould be due to the lower activity of the iridium when combined withrhenium.

    ______________________________________                                        Coke Levels on Spent Catalysts                                                Catalyst D     Catalyst E  Catalyst B                                         Pt         Ir      Pt + Re  Ir   Pt + Re                                                                              Ir + Re                               ______________________________________                                        Reactor 1                                                                              9.9   6.4      6.99  4.65  7.06  3.66                                Reactor 2                                                                             14.0   9.7     12.24  7.83 11.26  9.06                                Reactor 3                                                                             16.3   13.4    15.81  9.13 16.93  12.53                               ______________________________________                                    

Catalyst B results in higher C₅ + yields and hydrogen purity over thatof an unpromoted catalyst. Such a catalyst also shows considerable yieldstability, despite a lower activity over that of the trimetallicPt+Re/Ir catalyst (Catalyst E), due to the promotion of the iridiumcomponent. The higher C₅ + yields are obtained through lower C₁ -C₂production.

What is claimed is:
 1. A reforming process which comprises contacting areforming charge stock under reforming conditions with a catalystcomposition made up of a mixture of two components one componentcomprising a minor proportion of platinum and rhenium on a carbondioxide treated support and the second component comprising a minorproportion of iridium and rhenium on a separate carbon dioxide treatedsupport.
 2. The process of claim 1 wherein said support is an inorganicoxide.
 3. The process of claim 1 wherein said support is alumina.
 4. Theprocess of claim 3 wherein the platinum and iridium are present inamounts ranging from 0.05 to 5 weight percent of each of said metals andrhenium is present in an amount of from 0.2 to 0.6 weight percent. 5.The process of claim 4 wherein said platinum, iridium and rhenium areeach present in an amount of about 0.3 weight percent based on totalcatalyst composition.